1. Field of the Invention
The present invention relates to a liquid coating composition for forming an antireflective film deposited on top of a photoresist layer and to a photoresist laminate formed by making use of such a coating composition, as well as to a method for forming a photoresist pattern. More particularly, the present invention relates to a liquid coating composition for forming a top antireflective film, which, when used in the pattern formation process by the photolithography technique in which ArF excimer laser (with a wavelength of 193 nm) is utilized as activation light, can serve to reduce the multiple interference of light within the photoresist layer, thus ensuring high accuracy of the resulting photoresist pattern, and to a photoresist laminate using the composition, as well as to a method for forming a photoresist pattern.
2. Description of Related Art
As semiconductor devices are becoming ever more highly integrated, new techniques have been developed that are adapted to fine processing required in the production of semiconductor devices. The same is also true for the photolithography process, a key process in the production of semiconductor devices, where strong demand exists for further improvements in fine processing. To that end, various approaches have been attempted for forming ultrafine photoresist patterns by taking advantage of photoresist materials that function with short-wavelength radiations such as KrF, ArF, and F2 excimer lasers.
Recently, a significant amount of effort has gone into developing a ultrafine processing technique that employs activation light with a wavelength of 200 nm or shorter, in particular, ArF excimer laser light (193 nm in wavelength), and it has now become an important technical challenge to form even finer high-precision photoresist patterns by using particular photoresists that are adapted to be used with ArF excimer laser.
One known method designed to form photoresist patterns by means of photolithography involves deposition of an antireflective film (top antireflective film) on top of the photoresist film prior to exposure, and following development of the photoresist. In this manner, the multiple interference of light that takes place within the photoresist film can be prevented and, as a result, the variation in the width of the geometrical features of a photoresist pattern, which results from the variation in the thickness of the photoresist film, can be minimized.
In an effort to improve the above-described process, various proposals have been made concerning materials of the antireflective film and the photoresist film that are optimum for the formation of ultrafine patterns. For example, a technique described in JP-8-292565A employs as the antireflective film material a specific composition containing two different types of fluorine-based compositions. This technique has brought about a considerable improvement in the dimensional accuracy of the photoresist patterns without leading to an increase in the number of steps involved in the process or a reduction in the sensitivity of the photoresist. Another technique described in JP-10-3001A combines advantages of antireflectivity and stability of the coating over time. Each of these approaches, however, is directed to preventing the reflection in certain types of photoresists adapted to use with i-ray or g-ray, and none of them have proven effective when used in conjunction with the newly developed photoresists intended for use with ArF excimer laser. It is thus considered difficult to apply any of these conventional approaches to photoresist materials designed for use with ArF excimer laser to accurately form ultrafine photoresist patterns that are required in the production of today's integrated circuits.
On the other hand, certain types of photoresist materials, known as chemically amplified photoresists, have become increasingly used in photoresist film. A typical chemically amplified photoresist contains a base resin and an acid-generating agent which generates an acid upon exposure to radiation. Among known chemically amplified photoresist compositions, those that contain, as the base resin, a resin containing a (meth)acrylate unit that has at least one polycyclic hydrocarbon on its side chain and, as the acid-generating agent, an onium salt-based agent, in particular, one containing sulfonate ions, such as nonafluorobutane sulfonate ions and trifluoromethane sulfonate ions, are known to be suitable for use with ArF excimer laser.